Noises, Poor Performance, Easy Fixes, and Tune Up
1. What is that low-pitched somewhat
rumbling, intermittent sound coming from the front end of the
740 Turbo intercooled Volvo, especially at low speeds?
Well, I lived with that sound for years, even changing out the
front wheel bearings before I figured it out. It was the intercooler
fan (also known as the air-conditioning fan in some manuals)
in front of the intercooler (left, arrow, grille removed). The
inner keyway, if I remember correctly, had worn away on the fan
center housing so that it was no longer locked to the spline
on the rotating shaft (bottom left). So, the fan was running
independently of the shaft and making noises. Once I replaced
it with a good scrapyard fan, the noise stopped.
Turbochargers, driven by exhaust gases,
increase engine power and efficiency by forcing air into the
intake manifold under pressure. Set between the turbocharger
and intake manifold is the intercooler. The intercooler acts
as a heat exchanger to cool the compressed (heated) air from
the turbocharger, thus reducing the risk of detonation. After
all, in a gasoline engine, detonation is supposed to be initiated
from a spark rather than from superheated air, as in a diesel
2. Hiccupping (engine hesitates while car is driven). A possible
low-cost repair is to get the part from a junkyard. The advantage
is that you're not paying a lot of money for a suspected part
that may not be the culprit at all. The disadvantage is that the
junkyard part may not work.
Hiccups are hard to isolate because of their random, intermittent
occurrences. Some possible culprits:
a) If your car has trouble going up hills, all the while
spewing black exhaust smoke, the simplest possible fix is a new
air filter. This solution was all it took to correct the cause
for the aforementioned symptoms on my 740 Volvo Turbo.
replacing the fuel pressure regulator (arrow).
good option is replacing the fuel injection relay (arrow). Access
it by pulling out the ashtray and fuse cover plate, then remove
cigarette lighter shelf (Phillips screw beneath plastic snap-off
cover plate). Release and lift tray out. The fuel injection relay
has a white housing and is leftmost, second row behind fuse tray.
Gently pull up to remove from tray.
may well be the old, worn engine wiring harness. 1980 - 1987 Volvos
have wiring harnesses that degraded from engine heat after several
years of driving. This was especially prevalent in turbos because
of their higher heat output. The insulation would fall apart,
exposing bare wires, possibly leading to all sorts of gremlin-like
behavior. I recommend a new wiring harness or a very good used
one from a reputable dealer. A brand new one for the 740 Turbo
is ~$450 from IPD. The part is
expensive and the job is a bit involved. I haven't attempted it
yet. A good website about wiring harnesses is http://www.davebarton.com/volvoharnesses.html.
e) For those Volvos with a Hall sensor (see photo of Hall
plug below), a failing Hall sensor will give rise to hiccups.
Other symptoms include a no-start, wait a while, still no-start,
wait a while longer, and then engine finally starts. Lots of oil
on the Hall plug is a precursor to a failing Hall sensor. If you
see lots of oil on the Hall plug, I suggest pulling the whole
distributor out and replacing the big green O-ring before the
Hall sensor is short circuited. At the same time, check to see
that the feed wires to the Hall plug are still in good shape.
If they are, wipe oil from them. If the wires are not in good
shape, you may wish to consider replacing the Hall
3. My 240 Volvo doesn't start.
There are two simple checks to do first. Check fuse 6 or 7 (the
main fuel pump), depending on your year, to make sure it is intact.
If you don't hear the engine turn over, (a) check for 12 VDC across
battery terminals, and (b) clean the connections to the battery
posts and the ground cable connections, especially that at the
front wheel well (see Basics
of Diagnoses and Other Hints).
4. Tune Up: distributor cap and rotor replacement for in-line
Number the spark plug wires atop distributor, as shown, so that
you know where to connect each wire when done. (The camshaft
rotates clockwise as seen from front of engine looking backward.
The firing order is 1-3-4-2. If you opened up the cap, the clockwise
rotation of the rotor hits post contacts 1, 3, 4, 2, in that
order. The contacts inside the distributor cap can be identified
to each outside post by continuity tests. See below.)
It is difficult to get to the three 8-mm
bolts that hold the distributor cap in place. The easiest way
is to use an 8-mm ratcheting box-end wrench. If you don't have
that tool, the lower left and lower right bolts (as viewed from
front of engine) can be accessed with a small 1/4" drive
socket wrench. The middle top bolt, because the wire posts get
in the way, can be accessed with a 1/4" drive universal
Note position of old rotor before attempting
to take it off. You want to install new rotor in same position.
(At any rate, the nose of the rotor is aligned with the notch
in the distributor shaft.)
The old rotor is very difficult to get off. I broke the tail
end of this one by trying to pry it off with a single large flat-bladed
I've since come up with a better idea for getting the rotor off.
Fashion two sticks, tapered at one end as shown. The sticks are
about 6" long, ~1/2" wide, and 1/4" thick.
Insert tapered ends of the two sticks, one on each side of the
rotor shaft, and lift rotor off by levering the top ends of the
sticks. Makes life easier! By using sticks rather than screwdrivers,
you won't damage the rotor or the plastic cover plate underneath.
Before installing the new rotor, I sanded down the distributor
shaft with very fine sandpaper, wiped it clean, and lightly smeared
the shaft with silicone grease---all in the hope that the rotor
will release easier next time. When installing the new rotor,
align position as noted for old rotor, then rotate slightly each
way as you push down on it. You should hear an audible click
when it's properly seated.
The 1-3-4-2 firing order is readily apparent
from this photo. Run your own continuity tests from each exterior
post to each inside post to verify.